Your question doesn't make your intent clear, and that's apparent by the answers you're getting.
Title is off
Your title currently states
Make bootable Win8 USB on Ubuntu MacBook
That, when first reading, is very confusing as you mention three different operating systems at once. From your meta question here a more appropriate title might be
How can I dualboot Windows on an existing Ubuntu installation?
Digging further it appears you might already be dual booting Ubuntu on an Apple machine, so the question title might instead be
How can I triple boot Windows on an existing Ubuntu/Mac OSX setup?
Body is long and jumbled
Stories are good, but sometimes too much information isn't a good thing, try sticking more to the facts of the setup.
Some time ago, I bought a new HDD for my MacBook 2,1. I put it in and installed Ubuntu on it, using a CD. Everything went fine, didn't have to setup any special Apple stuff, didn't need to bless my partition, make an EFI partition, etc. Everything was done for me.
Recently, I found out that my DVD drive broke, though I'm not sure how it exactly happened. Anyway, I want to install Windows 8 Consumer Preview onto my MacBook, next to the Ubuntu install, preferrably using GRUB to load the Windows 8 bootloader. However, since my DVD drive is broken, the only way for me to be able to install it is to use a USB drive.
This is great, but reading it is difficult. Trying simplifying the statements and getting straight to the point:
I have a MacBook 2.1 with Ubuntu installed along-side OSX (Unless it's just Ubuntu, then drop the mention of Mac all together, it's not that important). I have have Windows 8 Consumer Preview on a USB drive, how can I install Windows 8 along side Ubuntu (and Mac OSX maybe) without losing access to my Ubuntu (and maybe Mac OSX partitions)
Same can be done with the next few paragraphs.
What is the question?
You later go on to state this, which is another source of confusion:
So my question is: how do I make a bootable USB drive for my MacBook so I can install Windows 8? And when that works, how do I get my GRUB back?
This contradicts what you mean to accomplish. So far you've gone to detail trying to install Windows 8 on this machine, but now you want to know how to make a bootable USB Drive for your MacBook then get you GRUB back. You're really asking two different questions here. How to make a bootable USB drive (in Ubuntu I assume) and how to get your GRUB back. So have you tried this and lost GRUB? There seems to be some vital information missing.
Try making the question more clear. State that you have Ubuntu installed and wish to dual boot Windows on it, what the procedure is for this, etc. To be honest it's been asked before so it'll likely end up being closed as a duplicate.
